1. Field of the Invention
The present invention relates to a method for controlling a driving input signal to efficiently utilize an ink jet head using shape memory alloy, and more particularly, the present invention relates to a method for optimizing a driving input signal in an ink jet head using shape memory alloy, which optimizes a waveform of a driving voltage applied to heat the ink jet head, without a structural alteration of the ink jet head driven by being heated and without a change in manufacturing processes for the ink jet head, thereby improving an ink firing characteristic and preventing the ink jet head from being overheated.
2. Description of the Related Art
Generally, printers are divided into a line printing type printer and a page printing type printer depending upon a printing scheme which they adopt. A so-called laser printer is representative of a page printing type printer, and a so-called dot printer or an ink jet printer is representative of a line printing type printer.
Drop-on-demand (DOD) type printer heads which fire liquid ink only under necessity are most widely used for ink jet printers. Use of such DOD type printer heads has gradually increased in that they require no electric charge or deflection of ink droplets and in that since high pressure is not needed, an easy printing is achieved by immediately firing ink droplets under atmospheric pressure.
Typical firing principles of such DOD type printer heads include a heating type firing method using a resistor, a vibration type firing method using a piezoelectric element, and a firing method using shape memory alloy, etc.
A printer head which adopts a heating type firing method generally includes a nozzle plate having a plurality of nozzles, a fluid passage plate coupled onto the nozzle plate and defining an ink storing chamber into which ink is stored, a substrate coupled onto the fluid passage plate and covering the ink storing chamber, and a heating resistor embedded into the substrate.
In an ink firing device of a printer head which adopts a heating type firing method, as shown in FIG. 1, ink is fired as described below.
First, if a predetermined voltage is applied to a heating resistor 14, heat is generated. By the heat generated in the heating resistor 14, air contained in ink adjacent the heating resistor 14 is expanded to create air bubbles. By these air bubbles, ink 16 inside an ink storing chamber 10 is forced out through a nozzle 12 to be fired toward a recording medium.
Accordingly, in the printer head which adopts the heating type firing method, bubbles such as lathers are generated when heat is applied to ink which is filled in the printer head, and the generated bubbles are fired through the nozzle to define a character on a printing sheet. Therefore, in the sense that the printer head uses air bubbles, the printer head is called an ink bubble jet type printer head.
However, the heating type firing method suffers from defects in that since ink is heated by heat generated in the heating resistor 14, the ink is likely to be chemically degraded, and this degraded ink may be deposited onto an inner surface of the nozzle 12 clogging the nozzle 12.
Also, since the heating resistor 14 repeatedly generates heat upon application of a voltage, a lifetime of the heating resistor 14 is shortened, and since only water soluble ink should be used, preserving property for a printed document is deteriorated.
A printer head which adopts a vibration type firing method, is generally similar in its structure to the printer head which adopts the heating type firing method, except that a piezoelectric element is disposed at a position where the heating resistor 14 is disposed in the printer head which adopts the heating type firing method (see FIG. 1).
In an ink firing device of a printer head which adopts a vibration type firing method, as shown in FIG. 2, ink is fired as described below. If predetermined electric power is supplied to a piezoelectric element 24, the piezoelectric element 24 vibrates. By the vibration of the piezoelectric element 24, a volume of an ink storing chamber 20 is momentarily changed, and by this, ink 26 inside the ink storing chamber 20 is forced out through a nozzle 22 to be fired toward a recording medium.
The vibration type firing method using the vibration of the piezoelectric element 24 provides an advantage in that since heat is not used, it is possible to use an ink other than water soluble ink and thereby a greater variety of choices are offered for ink. However, the vibration type firing method is encountered with problems in that since workability for the piezoelectric element 24 is impaired and especially, it is difficult to form the piezoelectric element 24, productivity is reduced.
FIG. 3 is a cross-sectional view schematically illustrating an ink firing device of a printer head which uses shape memory alloy. A shape memory alloy 32 which is in a flexurally deformed state is disposed above an ink storing chamber 30. If the shape memory alloy 32 which is in the flexurally deformed state is heated, the shape memory alloy 32 is returned to its original flattened state after a flexurally deformed portion is smoothed out.
As the shape memory alloy 32 is returned to its original flattened state, a volume of the ink storing chamber 30 is decreased, and according to this, ink supplied through an ink supplying path 38 and stored in the ink storing chamber 30 is fired through a nozzle 36 to a recording device (not shown).
A printer head using shape memory alloy is classified into a first type wherein several shape memory alloy layers having different phase transformation temperatures and different thicknesses are coupled one with another to be flexurally deformed and a second type wherein a shape limiting body 33 and the shape memory alloy 32 are coupled with each other to be flexurally deformed. At this time, a member comprising the shape limiting body 33 and the shape memory alloy 32 which are coupled with each other is called a vibrating plate.
Because printer heads of these types employ shape memory alloy of a plate-shaped configuration which has a thickness of 50-1,000 xcexcm and an area of 0.1-10 mm2, power consumption is increased upon heating, heating and cooling times are lengthened to decrease operation frequency, and printing speed is lowered thereby deteriorating practicality of the entire printer head.
Moreover, since the shape memory alloy layer is thick and wide, it cannot be instantaneously heated, and displacement is slowly generated over a relatively long period of time. Accordingly, due to the fact that a generated pressure is reduced, ink may not be fired or may not be properly fired. Also, even in the case that ink is fired, because firing speed of droplets is decreased, wetting may be caused and thereby it is difficult to achieve stable firing of the ink due to variations in velocity and size of ink droplets.
In addition, due to the fact that the shape memory alloy layer has a configuration of a plate which is large and thick and therefore, the entire structure thereof cannot but be enlarged, it is difficult to miniaturize the size of the printer head, integration density of nozzles is diminished and printing resolution is deteriorated.
In other words, in the case that the shape memory alloy is used as taught in the conventional art, a pressure chamber of the printer head must be enlarged such that it has a length of 100-10,000 xcexcm and a width of 50-500 xcexcm. Accordingly, if a pressure chamber of this size is used, the entire structure of the printer head cannot but also be enlarged.
Besides, since the printer head is constructed in that several shape memory alloy layers which are bonded one with another and bent, or a thin plate-shaped shape memory alloy layer and a shape limiting body which are bonded with each other and bent, are attached by bonding to a main body in which an ink storing chamber is defined, it is difficult to manufacture the printer head, and reliability is declined when the shape memory alloy is applied to the ink jet printer head which is required to be vibrated several ten million times.
Accordingly, as an efficient approach to improve ink firing capability, structures as shown in FIGS. 4 and 5 are disclosed in the art.
FIG. 4 is a plan view schematically illustrating an actuator section of an ink jet printer head using shape memory alloy, recently disclosed in the art, and FIG. 5 is a cross- sectional view schematically illustrating an ink firing device section of the ink jet printer head of FIG. 4.
In the ink jet printer head using shape memory alloy as shown in FIGS. 4 and 5, in order to shorten a heating time while reducing an amount of energy consumed upon heating and securing a volumetric displacement of a pressure chamber such that the volumetric displacement is sufficient to allow the ink jet printer head to fire ink, it is preferred that a width d of a vibrating plate is decreased and a length Lxe2x80x2 of the vibrating plate is increased. While it is generally preferred that a ratio of the width and the length of the vibrating plate is 1:1-1:7, the ratio can be changed depending upon a printer head used.
When observing operations of the ink jet printer head using shape memory alloy as shown in FIGS. 4 and 5, by the fact that a space part is defined by etching a portion of a substrate 40 to which a shape memory alloy 43 is attached, vibrating plates 41 and 43 are flexurally deformed due to a buckling phenomenon, by compression stress which is remained in a shape limiting body 41, that is, a silicon dioxide layer (SiO2), and are maintained in a flexurally deformed state. At this time, a member comprising the shape limiting body 41 and the shape memory alloy 43 which are bonded with each other, is called the vibrating plate. The shape limiting body 41 is generally made of SiO2, but a metallic material such as Si3M4, Si, poly silicon, etc. can be used to form the shape limiting body 41 while setting aside SiO2.
If electric power is supplied to the printer head, the electric power is applied to an electrode 44 to generate heat therein, and by the heat generated in the electrode 44, the shape memory alloy 43 which is maintained in the flexurally deformed state is heated. When being heated, the shape memory alloy 43 is willing to return to its original flattened state, and in this course of returning, a volume of a pressure chamber 50 is reduced to fire ink through a nozzle.
On the contrary, if the shape memory alloy 43 is cooled, since a flexural deformation is generated by residual compression stress of SiO2, a volume of the pressure chamber 50 is again increased, and ink is refilled by an amount which is fired.
At this time, because the silicon dioxide layer 41 which is formed on a surface of the substrate, has residual compression stress by which it is willing to flex by itself, it provides the shape memory alloy 43 with restoring force for enabling the shape memory alloy 43 flattened by being heated to be flexurally deformed again while being cooled.
Accordingly, in the printer head using shape memory alloy, these processes are repeated to continuously fire ink, thereby to complete a printing function.
In the ink jet printer head using shape memory alloy operated as described above, while the shape memory alloy layer 43 of the vibrating plate part has a flattened configuration in its original state, it has residual compression stress in the course of forming it as a film onto the substrate by a method such as deposition, etc. Accordingly, it is possible to change a magnitude of the residual compression stress which remains in the shape memory alloy 43, depending upon a deposition condition, and thermal treating temperature and time, etc. when carrying out deposition onto the substrate.
Therefore, most technical approaches for improving efficiency of an ink jet printer head using shape memory alloy by accomplishing adjustment and optimization of an ink firing amount and by preventing the printer head from being overheated, or the like, are related with a structural alteration of the ink jet head and a change in manufacturing processes for the ink jet head.
However, because these approaches for improving efficiency must be necessarily accompanied by modifications or alterations of entire processes or entire structures, although a simulation is performed with great precision, it is impossible to avoid errors by the time when they are perfectly applied in actual practice, and a lengthy period of time is needed to perfectly apply them in actual practice, whereby manufacturing cost is raised and a great deal of effort is required.
Accordingly, the present invention has been made in an effort to solve the problems occurring in the related art, and an object of the present invention is to provide a method for optimizing a driving input signal in an ink jet head using shape memory alloy, which optimizes a waveform of a driving voltage applied to heat the ink jet head, without a structural alteration of the ink jet head driven by being heated and without a change in manufacturing processes for the ink jet head, thereby improving an ink firing characteristic and preventing the ink jet head from being overheated.
In order to achieve the above object, according to one aspect of the present invention, there is provided a method for optimizing a driving input signal in an ink jet head using shape memory alloy, the ink jet head including a vibrating plate having a shape memory alloy layer and a silicon dioxide layer which are coupled with each other and formed such that it covers space parts which are formed left and right of a substrate, to be vibrated while being changed in its contour depending upon a temperature variation thereof, an electrode formed on the vibrating plate to have a desired pattern, an ink storing chamber defined between the space parts of the substrate for storing ink, a pressure chamber defined on the vibrating plate for containing ink, the pressure chamber discharging ink by vibration of the vibrating plate, a fluid passage defined by a fluid passage plate which is formed at a side of the pressure chamber, for allowing the ink stored in the ink storing chamber to flow into the pressure chamber, and a nozzle plate attached onto the fluid passage plate and being formed with a plurality of nozzles, for allowing ink to be fired in the form of droplets when the vibrating plate is vibrated, the method comprising the steps of: a first step of determining a voltage inputted when a maximum replacement generating time in the shape memory alloy layer disposed in the ink jet head using shape memory alloy is minimal, as a reference input voltage; a second step of measuring a first time from a reference input voltage supply starting point to a displacement starting point of the shape memory alloy layer; a third step of measuring a second time from after the first time measured in the second step to a point when a displacement of the shape memory alloy layer is maximal; a fourth step of determining a sum of the first and second times which are measured in the second and third steps, respectively, as a reference input voltage applying time; and a fifth step of determining a driving voltage through repeatedly applying different voltages which are less than the reference input voltage determined in the first step and measuring firing velocities and sizes of ink droplets which correspond to the respective voltages.
According to another aspect of the present invention, there is provided a method for optimizing a driving input signal in an ink jet head using shape memory alloy, the ink jet head including a vibrating plate having a shape memory alloy layer and a silicon dioxide layer which are coupled with each other and formed such that it covers space parts which are formed left and right of a substrate, to be vibrated while being changed in its contour depending upon a temperature variation thereof, an electrode formed on the vibrating plate to have a desired pattern, an ink storing chamber defined between the space parts of the substrate for storing ink, a pressure chamber defined on the vibrating plate for containing ink, the pressure chamber discharging ink by vibration of the vibrating plate, a fluid passage defined by a fluid passage plate which is formed at a side of the pressure chamber, for allowing the ink stored in the ink storing chamber to flow into the pressure chamber, and a nozzle plate attached onto the fluid passage plate and being formed with a plurality of nozzles, for allowing ink to be fired in the form of droplets when the vibrating plate is vibrated, the method comprising the steps of: a first step of establishing an input voltage and a voltage applying time such that a velocity of the vibrating plate disposed in the ink jet head using shape memory alloy is maximized; a second step of measuring a velocity and a size of ink droplets in the printer head, at the established input voltage and voltage applying time; a third step of determining whether or not the velocity and the size of ink droplets which are measured in the second step are optimal within design options; and a fourth step of establishing corresponding input voltage and voltage applying time as a waveform of a printer head driving signal when it is determined in the third step that the measured velocity and the size of ink droplets are optimal within the design options, and returning to the second step after reestablishing another input voltage and another voltage applying time when it is determined in the third step that the measured velocity and the size of ink droplets are not optimal within the design options.
According to another aspect of the present invention, there is provided a method for optimizing a driving input signal in an ink jet head using shape memory alloy, the ink jet head including a vibrating plate having a shape memory alloy layer and a silicon dioxide layer which are coupled with each other and formed such that it covers space parts which are formed left and right of a substrate, to be vibrated while being changed in its contour depending upon a temperature variation thereof, an electrode formed on the vibrating plate to have a desired pattern, an ink storing chamber defined between the space parts of the substrate for storing ink, a pressure chamber defined on the vibrating plate for containing ink, the pressure chamber discharging ink by vibration of the vibrating plate, a fluid passage defined by a fluid passage plate which is formed at a side of the pressure chamber, for allowing the ink stored in the ink storing chamber to flow into the pressure chamber, and a nozzle plate attached onto the fluid passage plate and being formed with a plurality of nozzles, for allowing ink to be fired in the form of droplets when the vibrating plate is vibrated, the method comprising the steps of: a first step of determining a voltage inputted when a replacement generating time in the shape memory alloy layer disposed in the ink jet head using shape memory alloy is minimal, as a reference input voltage; a second step of measuring a first time from a reference input voltage supply starting point to a displacement starting point of the shape memory alloy layer; a third step of measuring a second time from after the first time measured in the second step to a point when a displacement of the shape memory alloy layer is maximal; a fourth step of determining a sum of the first and second times which are measured in the second and third steps, respectively, as a reference input voltage applying time; a fifth step of calculating energy applied to the ink jet head, on the basis of the reference input voltage and the reference input voltage applying time which are determined in the first and fourth steps, respectively; and a sixth step of determining a waveform of a driving voltage by measuring a firing velocity and a size of ink droplets while variously controlling a voltage and a voltage applying time, such that energy less than the energy which is calculated in the fifth step is obtained.
According to still another aspect of the present invention, the sixth step comprises: a first process of determining a voltage applying time which corresponds to a firing velocity and a size of ink droplets of a printer head which is to be designed, such that energy less than the energy which is calculated in the fifth step is obtained, and calculating a voltage which corresponds to the voltage applying time; a second process of measuring a firing velocity and a size of the printer head, on the basis of the voltage and voltage applying time which are determined and calculated in the first process, respectively; a third process of determining whether or not data measured in the second process are optimal within design options; and a fourth process of establishing corresponding voltage and voltage applying time as a waveform of a printer head driving signal when it is determined in the third process that the measured velocity and the size of ink droplets are optimal within the design options.
According to yet still another aspect of the present invention, the sixth step further comprises: a fifth process of determining whether energy must be increased or decreased when it is determined in the third process that the measured velocity and the size of ink droplets are not within the design options; and a sixth process of returning to the second process after changing a driving voltage depending upon determination implemented in the fifth process.